1. Technical Field of the Invention
This invention relates to a light-emitting device using a light-emitting element capable of obtaining fluorescence or phosphorescence by applying an electric field to an element having a film containing an organic compound (hereinafter, described “organic compound layer”) provided between a pair of electrodes, and to a method for manufacturing same. The light-emitting device of the present invention refers to an image display device or light-emitting device using light-emitting elements. The light emitting device includes all of, for example, a module having a light-emitting element attached with a connector, e.g. anisotropic conductive film (FPC: Flexible Printed Circuit), TAB (Tape Automated Bonding) tape or TCP (Tape Carrier Package), a module having a printed board provided at an end of a TAB tape or TCP, and a module having an IC (Integrated Circuit) directly mounted on a light-emitting element by a COG (Chip On Glass) scheme.
2. Description of the Prior Art
The light-emitting element using an organic compound, having the features of thin and light weight, high-speed response, d.c. low-voltage driving, etc., is expected for the application to a flat panel display in the next generation. Particularly, the display device having light-emitting elements arranged in a matrix form is considered superior to the conventional liquid crystal display device in respect of its wide viewing angle and hence excellent visibility.
It is considered that the light-emitting element has a light-emission mechanism that, by applying a voltage to a pair of electrodes sandwiching an organic compound, the electrons injected from the cathode and the holes injected from the anode recombine at luminescent centers in an organic compound layer to form molecular excitons whereby the molecular exciton, upon returning to a ground state, gives off energy thus providing light emission. The excited state is known singlet excitation and triplet excitation. Light emission is considered possible to take place through any of the excitation states.
The light-emitting device, having such light-emitting elements arranged in a matrix form, can employ a drive method of passive matrix driving (simple matrix type) and active-matrix driving (active-matrix type). However, it is considered that, where the density of pixels increases, advantageous is the active-matrix type having switches on a pixel-by-pixel (or dot-by-dot) basis because of its capability of low voltage driving.
For the organic compound for an organic compound layer (exactly light-emitting layer) considered also as the core of light-emitting element, studies have being made on the smaller-molecular organic compounds and the polymer organic compounds. Attentions are drawn to the polymer organic compounds easier to handle and high in heat resistance than the smaller-molecular organic compounds.
There are known the spin coating technique, the ink-jet technique and deposition technique, as the methods to form a film of such an organic compound. In the case of using a polymer organic compound, it is a usual practice to carry out film forming by the use of the spin coating or ink jet technique.
However, the spin coating technique is to apply an application liquid by dripping it onto a substrate and then rotating the substrate at high velocity. This is excellent in respect of obtaining an even thickness of formed film. However, there is difficulty in delimiting the area of film forming. Hence, there is a drawback that a film can be formed only in one kind of organic compound on one substrate surface.
On the contrary, the ink jet technique is to apply an application liquid onto a film-forming area by the use of an ink head having an alignment mechanism. This, accordingly, allows for forming a film with using a plurality of kinds of organic compounds on one substrate surface, thus being excellent in realizing full-color display.
In the ink jet technique, however, where fabricating a full-color flat panel display with the light-emission colors of red, green and blue, there is a need of the exclusive units including a high-accuracy stage, an automated alignment mechanism and ink head.
Meanwhile, the ink jet technique is to eject and fly a polymer organic compound. Accordingly, in case the distance is improper between an application surface and an ink-jet head nozzle, there possibly occurs a problem of so-called curve fly, i.e. droplet arriving at unwanted point.
Furthermore, the ink jet scheme is to eject an ink containing an organic compound through a nozzle. Consequently, there arises a problem of nozzle clogging with an increased viscosity of ink. Contrary to this, where lowering the ink viscosity, lowered is the concentration of an organic compound contained in the ink, resulting in a reduced thickness of a formed film. Thus, there encounters a problem that the function is not available fully or increased frequency of ink ejection.
Concerning nozzle clogging, the problem is to be eliminated by increasing the nozzle diameter. This, however, includes a defect of making it impossible to provide patterning with precision, on the other hand.
It is noted that the curve fly and nozzle clogging as noted above are described in detail in Japanese Patent Laid Open No. 11-54270.
Meanwhile, when forming a pattern by using an ink jet method, in order to enhance film-forming accuracy there is also a need to form a bank with a height on a film-forming surface or making a surface treatment. Specifically, the substrate is exposed to a plasma to make only the bank surface ink-repellent, thus allowing ink to arrive at a desired point.
However, the ink jet technique, requiring the use of an ink-jet device as above, ink optimization and treating a film-forming surface, is not to be considered as a best suited film-forming method. There is a problem in easiness in the manufacture.
Therefore, it is an object of the present invention to enable film-forming of an organic compound layer in a desired position thereby forming an even film thickness of an organic compound layer when film-forming an organic compound layer of a polymer organic compound by using a spin coat technique, and further to form a plurality of organic compound layers on the same surface easier than the formation using the ink jet scheme.